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Variable Frequency Oscillator Sync with Digital Gap Detection

IP.com Disclosure Number: IPCOM000079422D
Original Publication Date: 1973-Jul-01
Included in the Prior Art Database: 2005-Feb-26
Document File: 2 page(s) / 28K

Publishing Venue

IBM

Related People

Shidler, KA: AUTHOR [+3]

Abstract

Previous binary data detection systems that incorporate variable frequency oscillators (VFO) have used analog gap sense circuitry to determine when a record contains data of a particular frequency, so that the VFO may be synchronized in proper phase with the data. The analog gap sensing circuits may be eliminated if the data record is properly formatted, and appropriate logic is included in the controller.

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Variable Frequency Oscillator Sync with Digital Gap Detection

Previous binary data detection systems that incorporate variable frequency oscillators (VFO) have used analog gap sense circuitry to determine when a record contains data of a particular frequency, so that the VFO may be synchronized in proper phase with the data. The analog gap sensing circuits may be eliminated if the data record is properly formatted, and appropriate logic is included in the controller.

The double frequency or frequency-modulated data record is coded with a leading sync field of all 0's (only clock bits recorded). The VFO counter 20 normally produces a clock window, so that the phase discriminator 10 only produces a phase-error pulse when an input pulse occurs in the clock window. These pulses in the clock window are interpreted as double-frequency clock pulses. When an external command requesting initial synchronization of the VFO is issued by the controller, the VFO drops the gating by the window and synchronizes to any data pulses in the data record. When a sync field is encountered, the VFO automatically synchronizes in the correct phase for data separation.

The presence of a sync field of clock bits only is recognized by the controller by an additional counter in the controller. When a pulse in the data record occurs in the clock window, the controller's counter advances one count. When a pulse in the data record occurs in the data window time, the controller counter is reset....